The present invention relates to an image forming apparatus using electrophotography such as a copying machine, a printer or a facsimile.
Also, the present invention relates to a toner transporting device which transports waste toner removed from an image bearing member by using a metal spiral member, and an image forming apparatus having the toner transporting device.
As an image forming apparatus, there is a type in which an electrostatic latent image is formed on an image bearing member such as a photoconductor, this electrostatic latent image is developed with toner. Then, a toner image is subjected to a first transfer onto an intermediate transfer belt. By repeating the above process each time the intermediate transfer belt rotates, multi layer transfer is performed on the intermediate transfer belt, and thereafter a full color image of four colors is subjected to a second transfer on a sheet material.
In this type image forming apparatus, when the toner image on the image bearing member is subjected to the first bias transfer on the intermediate transfer belt, the toner image is transferred onto the intermediate transfer belt by a bias applied to a transfer roller. At this time, it is necessary to keep appropriate and uniform a transfer pressure for pressing the transfer roller on the image bearing member through the belt. This reason is that: if the transfer pressure is too high, a hollow defect is produced in the toner image after transfer; and if the transfer pressure is too low, poor transfer is caused. Therefore, a type in which a transfer pressure controlling unit for pressing a first bias transfer roller is provided has been known (refer to JP-A-2001-194932).
However, JP-A-2001-194932 does not disclose how to attach the transfer pressure controlling means for the transfer roller to a frame of the intermediate transfer belt. Further, since a belt retreat mechanism and a belt tension mechanism are generally provided on the frame of the intermediate transfer belt, it is difficult to provide the transfer pressure controlling unit simply.
Further, waste toner removed from an image bearing member is transported to a discharge port by a toner transporting screw arranged in a waste toner transporting path (refer to JP-A-2001-228771). The screw has two types wound spirally, of which one is made of plastic, and of which the other is made of metal. The type in which the metal is wound has the following characteristics.
Since the waste toner can be uniformly transported to the discharge port little by little, clogging of the waste toner near the discharge port is difficult to occur.
Since the metal screw is more elastic than the plastic screw, resistance is difficult to be produced from a shape of the waste toner transporting path and a surface thereof.
The metal screw having such the characteristics includes problems of an unstable posture and vibration. Therefore, until now, the metal screw rotates while its both ends are fixed thereby to prevent the problems of the unstableness and the vibration.
Conventionally, using such the characteristics, the waste toner is transported. Regarding transportation of the waste toner, it is not preferable that the waste toner remains in the transporting path. Particularly, in a case that the waste toner remains near the discharge port (on the opposite side to a screw drive side), there are the following problems.
Clogging near the discharge port due to the residual waste toner.
Stain due to flying of the waste toner in exchange of a waste toner bottle or in cleaning in a cleaner.
Further, also in case that the waste toner remains near the drive side, the following problem is thought.
Waste toner leakage from a bearing part by drive vibration.
Since the above problems are caused, it is necessary to make the clearance amount between the screw and the transporting path side surface minimum thereby to reduce the residual toner in the transporting path as much as possible.
However, in a case that the clearance amount is small, the screw may rub strongly against the side surface of the transporting path at its both ends, which causes abnormal sound. As a cause of the strong rubbing, there are the following two factors.
Off-centering of screw in a nozzle (cap part of screw extending from a cleaner case to the outside.
Slack of screw produced by friction power between the off-center screw and the transporting path side surface.
A center position of the screw is determined by a center axis in the nozzle and the bearing without allowance (play). Therefore, in a case that decentering of the screw in the nozzle is produced by rotation of the screw, the pressure generated by the decentering is applied onto the transporting path side surface and the screw rubs against the transporting path side surface, so that the abnormal sound is generated. Further, the slack of the screw is caused by decentering, whereby the screw rubs against the transporting path side surface, so that the abnormal sound is generated. Since the screw is essentially decentered, in a case that the metal screw is used, it is necessary to take some measures for the factors of decentering.
Further, in an intermediate transfer system of an electrophotographic process, a toner image formed on a photoconductor is multi-layer transferred on an intermediate transfer medium (first bias transfer). A belt supported by plural roller or an intermediate transfer drum is used as the intermediate transfer medium. After transfer (second bias transfer) is performed from the intermediate transfer medium onto a transfer material, toner (residual toner) which is not transferred completely remains on the intermediate transfer medium. In a case that the transfer material is jammed because of any reason, a large amount of the toner remains on the intermediate transfer medium. In order to remove this residual toner, generally a blade or a brush is brought into contact with the intermediate transfer medium to scrape off the toner. The scraped-off toner is fed to a waste toner tank for storing the waste toner by a spiral rotator for transporting the waste toner which is located under the blade or the brush (JP-A-2001-228771).
However, in the constitution of the related example, under the blade or the brush, or at the inside of a cleaner which is a transporting path of the waste toner, the waste toner that has not been completely removed by only rotation of the spiral rotator remains. When the apparatus is violently moved in carriage under a state where the waste toner remains, the residual toner inside the cleaner flies up, so that the toner scatters inside the apparatus. This scattering is produced more severely by collision in the toner transporting path between the spiral rotator and the transporting path due to the vibration. In order to prevent this scattering, the blade or the brush comes into contact with the intermediate transfer medium when the apparatus stops, whereby the toner leakage can be prevented. However, in this case, the blade or the brush causes permanent strain, so that there is a problem that cleaning performance worsens. Further, when the severe vibration is forecasted, the intermediate transfer medium and the cleaner part may be detached from the apparatus body to perform cleaning. However, in this case, the operation becomes troublesome, so that there are also problems that cleaning cannot be performed sufficiently, the unit is broken with the detachment, and the intermediate transfer medium surface is stained by contact.